1. Field of the Invention
The present invention relates to a novel process for the preparation of 1-aminocyclopropanecarboxylic acid hydrochloride (ACC.multidot.HCl) ##STR2## from a cyclopropane-1,1-dicarboxylic acid diester of the formula 1: ##STR3##
2. Discussion of the Background
The amino acid 1-aminocyclopropanecarboxylic acid (ACC), which can be obtained readily from ACC.multidot.HCl by means of an ion exchanger, can be used for a large number of purposes. For example, ACC acts as a plant growth regulator by releasing the plant growth hormone ethylene when catalyzed by an enzyme. Moreover, ACC is employed as a unit in the synthesis of bactericides, fungicides and insecticides. It is therefore desired to find processes which produce ACC in a simple manner, in high yields and in high purity.
Compounds of the formula 1 can be prepared readily from malonic diesters and 1,2-dibromoethane or 1,2-dichloroethane.
SU 1,313,851 describes the synthesis of ACC starting from the diester 1 by the following Scheme I: ##STR4##
However, the process is very complicated, and the overall yield is low (approximately 50%). In step 1, the starting material is hydrolysed to give the 1,1-cyclopropanecarboxylic acid monoester 2, which is subsequently reacted with ammonia to give the monoamide 3. The sodium salt of ACC is then obtained by means of Hofmann degradation. The amino acid is obtained using ion exchangers.
This process has numerous disadvantages. Firstly, hydrolysis of the diester 1 to give the monoester 2 is very complicated. The diester is stirred with potassium hydroxide at room temperature for 2 days, and the pH is then brought to 1 using concentrated hydrochloric acid. The monoester 2 is then extracted using ethyl acetate. Secondly, the ethyl acetate has to be removed by distillation before the product is reacted with ammonia to give the monoamide 3. In addition, the yields of both reaction steps are only 89% and 83%, respectively. A further disadvantage of the process is the fact that the subsequent Hofmann degradation is carried out batchwise. This operating procedure is not feasible on an industrial scale when batches of a substantial size are used, since the exothermicity of the Hofmann degradation is uncontrollable. In this context, reference is made to DE-A-38 36 917.
A different synthesis, as described by T. A. Connors et al., J. Chem. Soc. 2129 (1960), leads to ACC via 4 steps: ##STR5##
This 4-step synthesis is complicated and involves intermediates which are difficult to manage. The bisamide 4 is sparingly soluble in water, while the bromine-containing product 5 is a highly unstable compound. The overall yield of this synthesis is as little as 35%.